Work begins on bringing pioneering 1940's computer back to life

Work has begun on rebuilding the UK's first fully operational general-purpose computer.

The Edsac - the Electronic Delay Storage Automatic Calculator, seen above - was completed in 1949 and used at Cambridge University to help research into areas including genetics, meteorology and X-ray crystallography.

UK computer conservation specialists this week produced the first replica components to rebuild the EDSAC. The rebuild will take place in public view at the National Museum of Computing at Bletchley Park in Milton Keynes, England, and is scheduled for completion in 2015.

The computer was built from 12 racks spread over 20 square metres. The racks held the more than 3,000 vacuum tubes it used to carry out instructions and the mercury-filled tubes that acted as its memory.

Edsac could carry out 650 instructions per second and had just 2KB of memory. While obviously orders of magnitude less powerful than a modern PC it effectively computed some 1,500 times faster than the mechanical calculators it replaced.

The machine's principal designer and creator sir Maurice Wilkes, seen here on the left, led the team that built the original Edsac for the Mathematical Laboratory at Cambridge University. Wilkes died in November 2010 at the age of 97.

Photo credit: Computer Laboratory, University of Cambridge

Edsac read programs from a punched paper tape and printed its results. Here you can see the machine's five hole tape reader and Creed teleprinter.

A key element of Edsac's design survives in computers to this day, the practice of storing both instructions and data in memory. The stored program concept was based upon the ideas devised by the brilliant mathematician John von Neumann in 1945.

Photo credit: Computer Laboratory, University of Cambridge

Edsac rebuild project manager Andrew Herbert said that EDSAC marked a change in what computers were used for, as the first computer to be used in scientific research.

"The late Professor Sir Maurice Wilkes, now widely regarded as the father of British computing, had the vision and the drive to realise the potential of computers to take on the mathematical calculations that underpin scientific research," he said.

"The impact of Edsac has been profound, so we aim to celebrate the achievements of its creators and to inspire future generations of engineers and computer scientists."

The machine's influence had an impact beyond the world of science, with the design of the Lyons Electronic Office, the first computer used in business, closely modelled on the Edsac.

Photo credit: Computer Laboratory, University of Cambridge

The Edsac was first operational in May 1949 and ran for nine years. Since it was scrapped only three of its 140 chassis have survived.

Above is a surviving Edsac chassis, which has been used to create a computer model for the replica chassis that will be used to rebuild the machine.

Photo: National Museum of Computing

A hole punch is used to produce the first of 20 replica chassis. The chassis were produced at Teversham Engineering Ltd in Cambridge this week.

Photo: National Museum of Computing

The Edsac recreation is being undertaken by Edsac Project volunteers at The National Museum of Computing in association with the Computer Conservation Society.

Funding is being provided by a consortium led by computing entrepreneur and Acorn co-founder Hermann Hauser, and includes a contribution from Google UK.

As those of us who once repaired granny's wireless set will know, the high voltage was a problem not so much for the valves as for the passive components. Insulating materials were not nearly as good as today, and they were usually based on shellac. Part of the skill of good design was ensuring that a fault such as a short-circuited blocking capacitor didn't take a cascade of valves with it. Draw grid current and the valve will soon be dead, and valves weren't cheap.
Mains transformers with 350-0-350 V secondaries would often go up in smoke.
I remember when working in medical research during the 1970s having to resurrect some old radioactivity counting gear. It had hundreds of valves, and of course those impressive power supplies. There was also a mercury delay line, presumably of the same design as the ones in the early computers.

I have one of the Univac chassis, sans no tubes. I'm not about to part with it as I've had it for 50 years. Along with a bunch of Honeywell parts from a unit that used the miniture vacuum tubes hard wired to a card. Computing power had to be close to a one second clock. Tubes don't respond as quickly as a semiconductor. Memory?? How about punched paper tape. A loop to load the booter, another for system and another for a 15 step program. Initially used to calculate the trajectory of artilary shells, it replaced a large mechanical computer (servos and gears).

It is a valiant aim. As the beginning of computer technology you can expect the modest computing power.
The very real problems running a machine of this kind are the voltages involved - none of your gentle 5v here! Valves run at high voltages - sometimes up to 400v. Oh, and they are prone to breaking down. Only replacing them was no easy matter with voltages like that flying around.
Something for all of us to remember when our handy laptops go wrong.

I serviced domestic radios etc thru the war capacitors and resistors were the biggest problem and the resistor problem was not really solved till the seventies, the introduction of all glass valve's introduced a new problem with poor contacts with the sockets (Russian ones were best with gold plated pins) with the all too familiar problem of having to bang the TV to make it work.

Most of the communications equipment I maintained early in my career operated at voltages well above 400V.
And replacing the tubes was an easy matter, as removing power stopped all that voltage "flying around".

I am sure that replacing tubes was a piece of cake.
Only shutting the system down three or four times a day to accommodate this will have had repercussions?
Oh, and I met those guys who tried changing them without shutting down to save time ... no visible scars but a few tales to tell.

if that often. Even our least reliable tubes were good for a month or two.
When we had to replace tubes, each section was separately powered, so we could shut them down individually. And attempting to replace a tube without removing power from the system either got you a reputation as the electronics tech equivalent to "script kiddie" or a very nice wake at which your former co-workers consumed mass quantities and stood around shaking their heads and saying "What an idjit."